Induction heating apparatus



April 14,

L. E. TICEHURST INDUCTION HEATING APPARATUS 'Filed $9pt. 19, 1956 22 f U HIGH ,8 2/ ggzggygg 527%? 4 58m; 33 4+ 8 22 44 1/ K I'NVENTOR 3 38 LAURENCE" E. T/csuu sr 36 BY [24M 4o ATTORNEY Unite S ate t fl "107' INDUCTION HEATING APPARATUS Laurence E. Ticeburst, Middleton, Mass., assignor to Raytheon Manufacturing Company, Waltham, Mass., a corporation of Delaware This invention relates to heating apparatus and more particularly to an induction heating device of the type in which a plurality of load objects to be heated are passed through either a single heating zone or a series of heating zones in which they are subjected to induced high-frequency currents.

In' induction heating apparatus of the type in which a series of load objects, commonly referred to as workpieces, are moved successively through or adjacent to high-frequency electric fields, usually generated by an inductive coil or coils coupled to a high-frequency power source, it has heretofore been difficult, if not impossible, to avoid high-voltage arcing, corona or other undesirable electrical effects resulting from the proximity of the highvoltage field producing coil to the conductive load object "being heat treated. As is known, for efficient power ,transfer from a stationary heating coil to a movable load object and for the rapid heating thereof, the load object must be accurately disposed adjacent to or within 'the inductive loop formed by the high-voltage heating coil. In addition, the mechanical and electrical difficulties involved in accurately prepositioning the highvoltage heating or bombing coil closely about each workpiece as it is carried through the heating zone by .a belt-driven device or conveyer are more readily understood when the workpiece is a tube or other evacuated device, held by top or bottom supports and requiring the bombing coil to be raised or lowered into the same rela- "tive position about each part or tube being bombed, and then withdrawn at accurately timed intervals by relatively complicated and expensive coil positioning and retracting apparatus. With this arrangement, the close and accurate positioning of high-voltage heating appara- Y impossible the duplication of heating results. The de-' sirability of being able to accurately position heating coils for substantially identical heating of a series of tube parts, getters, or for brazing, soldering or metal-to-glass ,sealing purposes and the like without the aforementioned i electrical and mechanical difliculties is, therefore, readily appreciated. g In accordance with the present invention, identical heating of a series of load objects which can be ac- "curately and easily positioned within the loop defined by a" heating coil is achieved by providing a high-current low-voltage inductive element comprising a metal plate having a first opening defining a first inductive link in which a conductive work load can be accurately fastened "at all times, a second opening in another portion of the metal plate forming a second inductive or pickup link, "and a slot extending between the two openings on the meta plate cut narrow to minimize fiux leakage therebetween and forming with the metal plate an inductive co upling which is made of sutliciently heavy metal to be *capab'le o'f carrying a heavy-heating current and of con- Patented Apr. 14,1959

centrating current in the region adjacent to the first inductive link, the metal plate being rotated or carried by conveying apparatus in a direction to permit the second inductive link to pass into relatively loose coupling with a stationary high-voltage coil. Thus, when a conductive load object is rapidly and easily fastened within the first opening in the metal plate where it remains accurately positioned and the second opening of the plate is passed through the field of the aforesaid stationary high-voltage coil, energy is inductively coupled from the stationary coil to the movable metal plate, and the load object is inductively heated by magnetic flux or lines of force which thread the first inductive link, while, at the same time, the danger of arcing from the high-voltage primary coil to the conveyer or to the movable load object carried by the conveyer is substantially eliminated.

The foregoing and numerous other features and advantages of the invention will best be understood from the following description of exemplifications thereof, reference being had to the accompanying drawings wherein:

Fig. 1 is a perspective view of the inductive element Fig. 2 is a side view of the inductive element shown in Fig. 1;

Fig. 3 is a top view of the primary coil;

Fig. 4 is a top view of the movable metal plate or inductive element shown in Fig. l; and

Fig. 5 is a partly structural and a partly diagrammatic view showing one arrangement of a conveyer device as used in an induction heating system in accordance with the present invention.

Referring now to Figs. 1 through 4, inclusive, wherein similar reference characters designate corresponding parts throughout, there is shown a high-voltage primary coil 10 divided into two spacially separated sections, each section comprising a plurality of turns 11, preferably of copper tubing, the turns being electrically connected in series by a vertically extending portion 12. The two oppositely disposed sections of primary coil 10 each comprise the same number of turns and are wound in the pancake fashion shown in Figs. 1 and 3 provided with a pair of coupling members 13 and 14 attached to the terminal portions 15 and 16 of the primary coil.

Referring again to Fig. 1, an inductive element 17 is concentrically arranged within the two sections of primary coil 10 to effect inductive coupling therebetween. The inductive element 17 in this embodiment of the invention is a metal plate, preferably of copper, of sulficient weight to carry a heavy heating current, and having a work receiving aperture 18 in which a conductive load element (not shown) can be easily and accurately fastened. At the opposite end of metal plate 17 isa second circular opening 19, as shown in Fig. 4, which forms a secondary inductive ring or pickup link-Q21 which is movable into a position to effect relatively loose inductive coupling, as shown in Fig. 2, with the high-voltage primary coil 10. The two apertures in "metal plate 17 are joined by 'a cut forming a slot 20 which extends between the apertures and divides the plate into two parallel conductor portions. The narrowness of slot 20 minimizes magnetic flux leakage between the conductor portions and insures that a high percentage of current generated in the pickup link or secondary inductive ring 21 travels along each conductor portion of plate 10 and is uniformly concentrated around the greatest work-receiving aperture 18 which defines a portion of conductive heating link 22 in'the metal plate 17.

To insure that the magnetic flux threads the work receiving aperture 18' uniformly and that the heating current is evenly concentrated around the entire periphery -of the inductive heating link 22, and particularly in a region adjacent to the slot 20, a pair of fiux concentrating slots 23 and 24 extend inwardly from the periphery of the metal plate 17 to a region adjacent to the junction of work receiving aperture 18 and slot 20, as shown in Figs. 1 and 4. With this arrangement, the current, which travels from the secondary inductive link 21 to the inductive heating link 22, is forced inwardly toward the region adjacent slot 20 and heating link 22 in a manner which provides for a high uniformity of flux threading the aperture 18 and the heating of the entire surface of a load object which acts in the nature of a shorted secondary element positioned within the work receiving aperture 18. It should be noted, however, that the flux concentrating slots 23 and 24 may be omitted when high uniformity of heating is not required. Thus, when an electron discharge device, the elements of which are to be heat treated, is easily positioned in the work receiving -',aperture 18, the flux concentrating slots 23 and 24, in connection with the metal plate 17, cause the maximum percentage of flux to thread the aforesaid elements to be heated for a given expenditure of energy and provide an even distribution of heat.

It should be understood that the terminal portions 15 and 16 of the high-frequency primary coil are electrically connected, in use, to a high-frequency generator (not shown) and to a cooling system, preferably water (not shown) by means of coupling members 13 and 14.

Also, for most efiicient heating, the load object should fit tightly into the Work receiving aperture 18, while it is not necessary that the secondary inductive ring or pickup link 21 be positioned in precise concentric alignment with the primary coil 10. Furthermore, the metal plate "17 can be connected directly to a grounded metal conveyor apparatus which transports both the load objects to be heated and the metal plate to a region adjacent to the magnetic field of primary coil 10, while, at the same time, the secondary inductive link 21 is sufiiciently isolated from the primary coil 10 that the danger of arcing and voltage breakdown is substantially eliminated.

Referring to Fig. 5, a practical embodiment of the invention, may, as shown, comprise a high-frequency generator 30 adapted to oscillate in the frequency region of 50 to 500 kilocycles to which is connected the highvoltage primary coil 10 positioned adjacent to the path of movement of inductive elements 17 which are attached by means of supporting members 33 to a conveyer 34. The conveyer 34, in turn, is mounted on a central vertical shaft 35 and receives intermittent rotary movement through bevel gears 36 and 37 from a source of power, such as, for example, an electric motor 38, which, as

' shown, is electrically connected by leads 39 and, 40 to a conventional timing switch 41 and to a source of alternating current. The timing switch 41 is also connected to the high-frequency generator 30 by leads 42 and 43. In operation, the neck portion 44 of each evacuated :workpiece 45 can be quickly inserted in the work receiving aperture 18 of each inductive element 17 mounted on the conveyor 34 and carried into inductive coupling with f primary coil 10. As shown, the workpieces may constitute partially completed electrical devices, such as electron tubes 45, each being connected to a vacuum pump (not shown) so that as the conveyor 34 rotates, the electron tubes are evacuated. The timing switch 41 actuates the electric motor 38 which rotates the conveyer to a position where the inductive link 21 is in concentric alignment with the two oppositely disposed sections of 'Within inductive heating link;.22. After the workpiece has been heated for, say seconds, the timing switch removes the A.-C. power from the high-frequency generator 3t and switches the power to, the electric motor 38 which, in turn, rotates conveyor 34 and removes the heated workpiece from the heating zone. Rotation of the conveyer also positions the succeeding inductive element 17 within the heating zone, and the timing switch 41 switches power from electric motor 38 to the highfrequency generator 30. In this manner, a plurality of workpieces are heated successively for equal periods of time.

In addition, a single workpiece or a plurality of Workpieces of diiferent sizes and shapes can be heated by providing either a single or a plurality of inductive elements having work receiving apertures of a sufi'icient size to accurately receive the workpieces being heated. Furthermore, it should be understood that the two section primary winding shown can be replaced by a single turn high-voltage primary when a comparatively lower coupling factor is desired; or, a plurality of high-voltage primary windings can be used to heat a single load object successively or a plurality of load objects simultaneously. Also, the inductive element 17 can be cooled by a single turn of copper tubing secured to the periphery of the metal plate which, as noted, can be connected to ground. While slot 20 in metal plate 17 is approximately one sixteenth inch in width, the slot can be made even smaller in width in order to attain more efiicient flux transfer from the secondary inductive link 21 to the inductive heating link 22. Furthermore, no special description has been given of the timing switch 41, the high-frequency generator 30 or the conveyer apparatus for moving the workpieces through the heating zone, because any of the usual means may be employed for producing this result. In addition, it will be appreciated that many variations of the features shown and described herein in connection with the single embodiment of the invention illustrated will occur to those who are skilled in the art to which the invention relates. It is, therefore, intended that the claims which follow shall not be limited by the particular details of the illustrated embodiment but rather by the prior art.

What is claimed is:

1. Apparatus comprising a primary induction coil adapted to be connected to a source of high-frequency current, a metal plate having a large opening in one portion and a small opening in another portion, a relatively narrow current concentrating slot connecting said openings to form a low-voltage high current conductive loop, said large opening positioned adjacent to said primary induction coil to efiect inductive coupling therebetween, and a pair of flux concentrating slots extending from the periphery of said metal plate to a region adjacent to the junction of said slot and said first aperture.

2. Apparatus comprising a primary induction coil, 2. source of high-frequency current, means for connecting said primary induction coil to said source, a single metal plate having first and second apertures therein and a current concentrating slot connecting said apertures to form an inductive element, means for moving said first aperture in said metal plate adjacent to said primary induction coil for a predetermined time interval to etfect inductive coupling therebetween, said second aperture adapted to receive a grounded metallic load object to be heated by said high-frequency current.

3. Apparatus comprising a primary induction coil, a source of high-frequency current, means connecting said primary induction coil to'said source, a metal plate having first and second apertures therein and a slot connecting said apertures to. form an inductive element, "a pair of flux concentrating slots extending from the periphery of said inductive element to a region adjacent to the junction of said slot and said first aperture, and means for moving said second aperture in said metal plate adjacent to said primary induction coil to effect inductive coupling therebetween.

4. Heating apparatus comprising means for establishing a first high-frequency field including aprimary coil, an

inductive element comprising a metal plate having a first circular opening forming a secondary inductive link in one portion of said metal plate, a second circular opening forming a high-current low-voltage primary inductive link in another portion of said metal plate, a current concentrating slot extending in said metal plate from said primary to said secondary inductive link, a conductive Work load defining a shorted secondary element inserted in said primary inductive link, apparatus for moving said first circular opening in said inductive element adjacent to the high-frequency field formed by said primary coil, and timing means for halting for a predetermined time said inductive element adjacent to said high-frequency field.

5. Apparatus comprising means for establishing a highfrequency field, a movable one-to-one turns ratio inductive element comprising a single metal plate for establishing a second high-frequency field of low-voltage high current, means for accurately positioning a grounded conductive load element capable of absorbing electrical energy in said second field, and means for moving said inductive element through said first field to elfect inductive coupling therebetween at predetermined time intervals.

6. Apparatus for the induction heating of a plurality of load objects comprising a plurality of primary induction coils, means to apply a high-frequency current to said primary induction coils, a low-voltage high-current secondary inductive element comprising a single metal plate having first and second apertures therein, a current concentrating slot in said metal plate extending from said first aperture to said second aperture to form a highcurrent low-voltage conductive lead linking said apertures, said first aperture adapted to receive a conductive load object to be heated, said second aperture forming a single conductive link, apparatus for moving said conductive link progressively into inductive coupling with said primary induction coils, and timing means halting the motion of said conductive link for predetermined time intervals.

7. Apparatus for the induction heating of a plurality of single turn high-current low-voltage load elements comprising a primary inductive element and a plurality of secondary inductive elements, each of said secondary inductive elements comprising a single metal plate having a voltage pick-up aperture and an aperture therein adapted to receive a conductive load element to be heated, a slot connecting said apertures to form a single conductive loop, a source of high-frequency alternating current, means connecting said primary inductive element to said source of high-frequency alternating current, conveyor means for moving said secondary inductive elements along a predetermined path progressively into coaxial alignment with said primary inductive element to efiect inductive coupling therebetween, and separate timing means coacting with said conveyor means for halting said secondary inductive elements in said coaxial alignment at predetermined time intervals.

8. Power transfer apparatus comprising means for establishing a first magnetic field, a single metal plate inductive element adapted to produce a low-voltage high current magnetic field, means for supporting a grounded conductive load object within the magnetic field established by said inductive element when said inductive element is positioned in said first magnetic field, means for moving said inductive element out of inductive coupling with said first magnetic field after a predetermined time interval, and a grounded metallic support connected to said inductive element to remove therefrom any voltage gradient with respect to ground due to the proximity of high-voltage means.

9. In combination, an inductive element for the induc tion heating of a conductive load object, said inductive element comprising a single metal plate having a load receiving aperture and an aperture forming a low voltage inductive link therein, a transverse slot intermediate the end portions of said metal plate connecting said apertures to form a single conductive loop, a primary induction coil adapted to be connected to a source of high-frequency current, conveyer apparatus supporting said inductive link adjacent to said primary coil, and separate timing means independently coacting with said conveyer apparatus for moving said inductive link through the field of said primary coil at predetermined time intervals.

10. An apparatus as set forth in claim 9 wherein a metal cooling coil extends around the periphery of said metal plate.

11. An apparatus as set forth in claim 9 wherein said load object has a circular cross section and wherein the aperture in said inductive element has a circular portion adapted to receive said circular load object.

12. Power transfer apparatus comprising a stationary primary coil, means to supply said primary coil with a high-voltage high-frequency current, a high-current inductive element having an aperture of circular cross section therein of a diameter sufficient to support in close fitting relation a low-voltage grounded load element, a grounded metallic arm attached to said inductive element, and conveyor means for moving said high-current inductive element along a predetermined path into inductive coupling with said primary coil.

13. Power transfer apparatus comprising a stationary primary coil, means to supply said primary coil with high-frequency current, a low-voltage high-current inductive element having an aperture of circular cross section therein adapted to support in close-fitting relation a circular grounded load object, a grounded metallic arm attached to said inductive element, and means for moving said metallic arm along a predetermined path to carry said inductive element into inductive coupling with said primary coil.

14. Power transfer apparatus comprising a stationary high-voltage primary coil, means to supply said primary coil with a high-voltage high-frequency current, a lowvoltage high-current inductive element comprising a single metal plate having a first aperture therein defining a coupling link, a second aperture of circular cross section adapted to support in close-fitting relation a load element to be heated thereby, a current concentrating slot connecting said apertures, a metallic support holding said coupling link of said inductive element adjacent to said primary coil to effect inductive coupling therebetween and means for grounding said metallic support to remove therefrom any voltage gradient with respect to ground caused by the proximity of said high-voltage primary coil.

References Cited in the file of this patent UNITED STATES PATENTS 2,109,323 Smith Feb. 22, 1938 2,650,290 Newhouse Aug. 25, 1953 2,785,265 Salisbury Mar. 12, 1957 FOREIGN PATENTS 706,489 Great Britain Mar. 31, 1954 

